1. Field of the Invention
This invention relates to an improvement in plasma etching and particularly to an enhancement in the etch rate of plasma etching processes employing plasmas produced from a gaseous organohalide compound.
2. The Prior Art
In recent years, in the field of surface processing of substrates such as organic polymers and semiconductors, the conventional wet processing method has been extensively replaced by a dry etching processing method. In this so-called dry etching technique, the surface to be etched is exposed to a plasma established by a high frequency glow discharge. For example, U.S. Pat. No. 3,795,557 (Reissue 30,505) discloses exposing a semi-conductor material such as Si, GaAs, GaAsP, InSb having a relatively thin (200 to 10,000 Angstroms) layer of a dielectric material e.g. SiO, SiO.sub.2, Si.sub.3 N.sub.4, either deposited or thermally grown onto the semiconductor, to a gaseous plasma formed from a binary mixture consisting essentially of oxygen and an organohalide compound such as tetrafluoromethane (CF.sub.4), the mixture containing 1 to 75 percent oxygen by volume, for an extended period of time. Other patents which contain similar teachings of plasma etching under steady state conditions using organohalide/oxygen mixtures include U.S. Pat. Nos. 4,174,251, 4,180,432, 4,374,699, and 4,487,652. U.S. Pat. Nos. 4,357,203, 4,460,436 and 4,482,427 are exemplary of prior art use of O.sub.2 being the sole constituent of a plasma etchant. U.S. Pat. No. 4,487,652 further teaches the use of an oxygen plasma under steady state conditions to clear underlying photoresist and polyimide layers which remain on a substrate after plasma etching of the overlying oxide and a part of the photoresist and polyimide layers with an organohalide/oxygen mixture is completed.
One drawback to the use of organohalide/oxygen mixtures is oftimes the gaseous mixture halogenates the surface of the substrate undergoing plasma etching and forms a halogen contaminated film surface on the substrate. The formation of the halogenated film, or the existence of a halogen contaminated substrate surface, slows the etch rate of the plasma and thereby unduly prolongs the time required for etching (Anand, M. et al, Polymer, 20(2, 507, 1979). Further, the presence of the halogen contaminated surface may also interfere with subsequent processing steps which are intended for the etched substrate, e.g. plating, lamination and adhesion to other later applied layers of organic or inorganic materials.
Another drawback to the use of dry plasma etching has been that for a particular system, i.e. polymer to be etched, etchant gas, and operating conditions, there is a steady state etch rate that limits the maximum etch rate. That is, previous plasma etching operations have been conducted under steady state conditions which has meant that the etch rate was effectively controlled, by the composition of the etchant gas.
Because of the demand for ever-higher speeds of operation and the need for reliably prepared semiconductor components, there has been a considerable effort in the electronics industry to resolve the halogenated surface film problem. We have discovered a plasma etching process employing the use of different gaseous plasma compositions for dry etching which appears to substantially eliminate the etch rate inhibiting halogen surface film previously encountered with organohalide containing plasmas and to produce etch rates substantially greater than the conventional steady state etch rates previously obtained. The plasma etching process of the present invention facilitates, in particular, the process of etching organic polymeric substrates at an extremely rapid rate that is much higher than any encountered in the prior art by using the etching properties of the halogen containing surface layers.